1. Field of the Invention
The present invention relates to a shift register and a liquid crystal display (LCD) having the same, and more particularly to a shift register for improving reliability and life span thereof and a liquid crystal display having the same.
2. Description of the Related Art
In these days, information processing devices have been rapidly developed in a trend with various architectures, functions and faster information processing speed. Information processed in those information-processing devices has an electrical signal format. In order to visually confirm information processed in the information-processing device, a display for a role as an interface should be provided.
LCDs have advantages such as the lighter weight, small size, high resolution, lower power consumption and friendly relation with environment and they render display of full colors compared with the traditional cathode ray tube (CRT). Such the advantages allow the LCDs to replace the CRTs and to be spotlighted as a next generation display.
LCDs apply an electric power to liquid crystal having a specific molecular configuration to vary the molecular arrangement of liquid crystal. The variation in the molecular configuration of liquid crystal causes a variation in optical properties such as birefringence, optical rotary power, dichroism, light scattering. The LCDs utilize such variations in optical properties to display an image.
The LCD device is largely classified into a TN (Twisted Nematic) type and a STN (Super-Twisted Nematic) type. The liquid crystal display device is, according to the driving method, classified into an active matrix display type, which uses a switching device and a TN liquid crystal, and a passive matrix type, which uses an STN liquid crystal.
A distinguishable difference of two types is in that the active matrix display type is applied to a TFT-LCD that drives the LCD by using a TFT and the passive matrix display type dispenses with a complicated circuit associated with a transistor because of using no transistor
TFT-LCD is divided into amorphous silicon TFT LCD (a-Si TFT-LCD) and polycrystalline silicon TFT LCD (poly-Si TFT-LCD). Poly-Si TFT-LCD has advantages of lower power consumption, lower price compared with a-Si TFT-LCD but has a drawback in that its manufacturing process is complicated. Thus, poly-Si TFT-LCD is mainly used in a small sized display such as mobile phones.
Amorphous-Si TFT-LCD is applied to a large screen sized display such as notebook personal computer (PC), LCD monitor, high definition (HD) television, etc., due to easy application of large screen and high production yield.
FIG. 1 is a simplified schematic view showing a conventional TFT substrate in a poly-TFT LCD. FIG. 2 is a simplified schematic view showing a conventional TFT substrate in an amorphous-TFT LCD.
As shown in FIG. 1, the poly-Si TFT LCD includes a data driving circuit 12 and a gate driving circuit 14 disposed on a glass substrate 10 having a pixel array. A terminal part 16 is connected to an integrated printed circuit board (PCB) 20 by using a film cable 18. Those structures may save the manufacturing costs of products, minimize the power-loss due to the integration of driving circuits and provide a display device having a slim design.
However, as shown in FIG. 2, a-Si TFT LCD has a data driving chip 34 formed on a flexible PCB 32 in a manner of COF (Chip-On-Film). A data PCB 36 is connected to a data line terminal of the pixel array through the flexible PCB 32. A gate driving chip 40 is formed on a flexible PCB 38 in the manner of forming a COF. A gate PCB 42 is connected to a gate line terminal through the flexible PCB 38.
That is, a-Si TFT LCD has disadvantages such as high cost and large size in aspects of cost and structure in comparison with those of poly-Si TFT LCD.